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United States Patent |
6,197,423
|
Rieder
,   et al.
|
March 6, 2001
|
Micro-diastrophic synthetic polymeric fibers for reinforcing matrix
materials
Abstract
Exemplary mechanically-flattened fibers of the invention comprise generally
elongate bodies having varied width or thickness dimensions and
micro-diastrophic surface deformities. Preferred fibers are elongate
synthetic polymer or multipolymer blend fibers for reinforcing matrix
materials such as concrete, shotcrete, gypsum-containing materials,
asphalt, plastic, rubber, and other matrix materials. Preferred methods
for manufacturing such fibers comprise subjecting synthetic polymer fibers
to compressive forces sufficient to achieve flattening and surface
micro-diastrophism without substantially shredding and abrading the
fibers.
Inventors:
|
Rieder; Klaus-Alexander (Boxborough, MA);
Berke; Neal S. (North Chelmsford, MA);
Fyler; Stephen J. (Fremont, NH)
|
Assignee:
|
W. R. Grace & Co.-Conn. (New York, NY)
|
Appl. No.:
|
416012 |
Filed:
|
October 8, 1999 |
Current U.S. Class: |
428/397; 428/400 |
Intern'l Class: |
D01F 003/00 |
Field of Search: |
428/397,400,175
|
References Cited
U.S. Patent Documents
3953953 | May., 1976 | Marsdon | 42/659.
|
4297409 | Oct., 1981 | Hannaht | 428/247.
|
4297414 | Oct., 1981 | Matsumoto | 428/400.
|
4414030 | Nov., 1983 | Restrepo | 106/90.
|
4451534 | May., 1984 | Akagi et al. | 428/400.
|
4522884 | Jun., 1985 | Brody | 428/400.
|
4565840 | Jan., 1986 | Kuhayashi et al. | 524/8.
|
4764426 | Aug., 1988 | Nakamura et al. | 428/400.
|
4792489 | Dec., 1988 | Kakiuchi et al. | 428/400.
|
5298071 | Mar., 1994 | Vondran | 106/757.
|
5298313 | Mar., 1994 | Noland | 428/400.
|
5753368 | May., 1998 | Berke et al. | 428/375.
|
5882322 | Mar., 1999 | Kim et al. | 428/175.
|
5897928 | Apr., 1999 | Sanders et al. | 428/36.
|
5985449 | Nov., 1999 | Dill | 428/399.
|
5993537 | Nov., 1999 | Trottier et al. | 106/724.
|
6045911 | Apr., 2000 | Legrand et al. | 428/400.
|
6048613 | Apr., 2000 | Yamakawa et al. | 428/400.
|
Foreign Patent Documents |
60-186448 | Sep., 1985 | JP.
| |
WO 99/36640 | Jul., 1999 | WO.
| |
WO 99/46214 | Sep., 1999 | WO.
| |
Other References
State-of-the-Art Report on Fiber Reinforced Concrete, ACI Journal, Nov.
1973, pp. 729-744.
Synthetic Fiber For Industry, Whiting Company, 1990, pp. 1-6.
|
Primary Examiner: Edwards; N.
Attorney, Agent or Firm: Leon; Craig K., Baker; William L.
Claims
It is claimed:
1. Fibers for reinforcing matrix materials, comprising: a plurality of
mechanically-flattened fibers having generally elongate bodies comprised
of at least one synthetic polymer, said bodies having an average length of
5-75 mm., an average width of 0.5-8.0 mm., and an average thickness of
0.005-3.0 mm.; the average fiber width of said mechanically-flattened
fibers exceeding the average fiber thickness; said fiber bodies having
irregular and random displacements of polymer material on the fiber
surface, said fiber surface displacements comprising microscopic
noncontinuous stress fractures and microscopic elevated ridges.
2. The fibers of claim 1 wherein said fibers comprise at least one
polyolefin.
3. The fibers of claim 2 wherein said fibers comprise at least two
polymers.
4. The fibers of claim 1 wherein said fibers comprise polypropylene,
polyethylene, polystyrene, or a mixture thereof.
5. The fibers of claim 4 wherein said fibers comprise polypropylene.
6. The fibers of claim 1 wherein said fibers comprise a polyolefin, nylon,
polyester, rayon, acrylic, polyvinyl alcohol, or a mixture thereof.
7. The fibers of claim 1 wherein said fibers comprise polypropylene,
polyethylene, or a mixture thereof.
8. The fibers of claim 1 wherein said fibers comprise at least two
polymers, said fibers being fibrillatable when agitated in a hydraulic
cementitious composition.
9. The fibers of claim 1 wherein said fibers are monofilament,
multi-filament, collated fibrillated, or ribbon form.
10. The fibers of claim 1 having two or more polymers of different
molecular weights.
11. The fibers of claim 1 comprising fibers mechanically flattened
intertwined.
12. The fibers of claim 1 comprising fibers mechanically flattened
interwoven.
13. The fibers of claim 1 wherein said fiber width varies by at least 10%
along the length of the fibers.
14. The fibers of claim 1 wherein said fibers have ends, said fiber ends
having widths exceeding the average fiber width.
15. The fibers of claim 1 wherein said fiber surface displacements resemble
glacial erosions.
16. The fibers of claim 1 wherein said surface of said fibers have a
smeared appearance when viewed with the aid of a microscope.
17. The fibers of claim 1 wherein said ridges have varying elevations that
have different shading when viewed with the aid of a microscope.
18. The fibers of claim 1 wherein, in said plurality of fibers, fibers are
provided in the form of bundles cut from a mechanically flattened
intertwined rope of fibers.
19. The fibers of claim 1 wherein said fibers are packaged in packaging
operative to dissolve or disintegrate when introduced into concrete.
20. The fibers of claim 1 wherein said fibers are coated.
21. The fibers of claim 1 wherein said fiber surfaces are substantially
free of embedded cement particles.
22. The fibers of claim 1 wherein said fibers are substantially free of
shredding.
23. The fibers of claim 1 wherein portions of the flattened fibers have
less translucency due to internal or superficial flattening stresses.
24. Fibers for reinforcing matrix materials, comprising: a plurality of
mechanically-flattened fibers having generally elongate bodies comprised
of at least one synthetic polymer, said bodies having an average length of
5-75 mm., an average width of 0.5-8.0 mm., and an average thickness of
0.005-3.0 mm.; the average fiber width of said mechanically-flattened
fibers exceeding the average fiber thickness; said fiber bodies having
irregular and random displacements of polymer material on the fiber
surface, said fiber surface displacements comprising microscopic
noncontinuous stress fractures and microscopic elevated ridges; said
irregularity and randomness of polymer material displacements occuring on
the surface of individual fibers as well as from fiber to fiber.
25. The fibers of claim 24 wherein said fibers are cut from a flattened
intertwined rope of fibers.
26. The fibers of claim 25 wherein said fibers are bundled together.
27. The fibers of claim 25 wherein said fibers are coated.
Description
FIELD OF THE INVENTION
This invention relates to synthetic polymer fibers useful for reinforcing
matrix materials, and more particularly to fibers having
micro-mechanically-deformed morphologies useful for enhanced performance
in matrix materials such as asphalt, rubber, plastic, or in such matrix
materials such as ready-mix concrete, shotcrete, bituminous concrete,
gypsum compositions, or other hydratable cementitious compositions; to
matrix compositions containing such fibers; and to methods for treating
fibers and for modifying matrix materials.
BACKGROUND OF THE INVENTION
Although the fibers of the present invention are believed suitable for
reinforcing a number of matrix materials, such as adhesives, asphalt,
composites, plastic, rubber, etc. and structures made therefrom, they are
primarily intended for reinforcing hydratable cementitious compositions
such as ready-mix concrete, precast concrete, masonry concrete, shotcrete,
bituminous concrete, gypsum compositions, gypsum- and/or Portland
cement-based fireproofing compositions, and other hydratable cementitious
compositions. A major purpose of the fibers of the present invention is
reinforcing concrete (e.g., ready-mix, shotcrete, etc.) and structures
made from these. The task of reinforcing matrix materials such as these
poses one of the greatest challenge for designers of reinforcing fibers.
Concrete is made using a hydratable cement binder, a fine aggregate (e.g.,
sand), and a coarse aggregate (e.g., small stones, gravel), and is
consequently a brittle material. If a concrete structure is subjected to
stresses that exceed its maximum tensile strength, then cracks can be
initiated and propagated in the concrete. The ability of a concrete
structure to resist crack initiation and crack propagation can be
understood with reference to the "strength" and "fracture toughness" of
the fibers.
Fiber "strength" relates to the ability of a cement or concrete structure
to resist crack initiation. In other words, fiber strength is proportional
to the maximum load sustainable by the structure without cracking, and is
a measurement of the minimum load or stress (e.g., the "critical stress
intensity factor") required to initiate cracking in that structure.
On the other hand, "fracture toughness" relates to the specific "fracture
energy" of a cement or concrete structure. This concept refers to the
ability of the structure to resist propagation--or widening--of an
existing crack in the structure. This toughness property is proportional
to the energy required to propagate or widen the crack (or cracks). This
property can be determined by simultaneously measuring the load required
to deform or "deflect" a fiber-containing concrete (FRC) sample at an
opened crack and also measuring the amount or extent of deflection. The
fracture toughness is therefore determined by dividing the area under a
load deflection curve (generated from plotting the load against deflection
of the FRC specimen) by its cross-sectional area.
In the cement and concrete arts, fibers have been designed to increase the
strength and fracture toughness in reinforcing fibers. Numerous fiber
materials can be used for these purposes, such as steel, synthetic
polymers (e.g., polyolefins), carbon, nylon, aramid, and glass. The use of
steel fibers for reinforcing concrete structures remains popular due to
the inherent strength of the material. However, one of the concerns in
steel fiber product design is to increase their "pull out" resistance
because this increases the ability of the fiber to defeat crack
propagation. In this connection, U.S. Pat. No. 3,953,953 of Marsden
disclosed fibers having "J"-shaped ends for resisting pull-out from
concrete. However, stiff fibers having physical deformities may cause
entanglement problems that render the fibers difficult to handle and to
disperse uniformly within a wet concrete mix. More recent designs,
involving the use of "crimped" or "wave-like" polymer fibers, may have
similar complications, depending on the stiffness of the fiber material
employed.
U.S. Pat. No. 4,414,030 of Restrepo disclosed the use of microfibrillated
polyolefin filaments that are oriented in all spatial directions by
subjecting fibrillated ribbons to air, thereby spreading out the separate
fibers, and then feeding these separated fibers into a mortar mixing
machine fitted with a high-speed propeller to blend the mortar components
and fibrous materials together. The mechanical shredding action which
takes place in the mixing operation causes the ribbons to become further
fibrillated, such that the ribbon fibrils are broken apart into individual
filaments having a branched structure with microfibrils outwardly
projecting along their length. The projected microfibrils are somewhat
curled in shape and perform as anchoring elements or "hooks" within the
cement hardened matrix. It is generally believed that side branches or
"hooks" can act to resist fiber dislodgment or pull-out from the cement
matrix and present enlarged surface area for anchoring within concrete.
The physical branched fiber structure would appear to create entanglement
problems that would render handling and dispersion within a wet concrete
mix somewhat difficult to achieve.
U.S. Pat. No. 5,753,368 of Berke et al. taught fibers having a glycol
ether-based coating for enhancing bond strength of the fibers within
concrete. Berke et al. further taught that the fibers could be bundled
using mechanical or chemical means, and that the fibers could be
introduced into a cement composition using packaging technology to
facilitate mixing and dispersion within concrete. This technology may be
applied to varieties of fibers and shapes to enhance pull out resistance
while facilitating uniform dispersion within the concrete mix.
U.S. Pat. No. 5,298,071 of Vondran discussed the problem of achieving a
uniform dispersal of fibers within a wet cement mix. Vondran noted that
fibers were typically added to the mixer with the cement, sand, aggregate,
other admixtures, and water. His approach was to add fiber precursors
(e.g., steel fibers and polyolefin in the form of extruded monofilament or
fibrillated sheet fiber) and cement clinker to a ball mill grinder and to
obtain a hydratable mixture comprising interground fibers in a dry
hydratable cement powder that could then be used for making the concrete
structure.
It is readily observed that Vondran's clinker/fiber-intergrinding method
(hereinafter the "Vondran method") purports to achieve quick fiber wetting
and uniform dispersion without the balling and clumping found when adding
the fiber components separately into concrete. The present inventors,
however, observe that the Vondran method teaches that "fiber precursors"
are combined with cement clinker particles into a ball mill cement
grinder, and that this process provides fibers that are "attenuated,
roughened and abraded by the action of the clinker particles and the
grinding elements on the fiber" (See U.S. Pat. No. 5,298,071 at column 2,
lines 58-66). This process purportedly results in improved mechanical
bonding between the cement and fibers.
In the present invention, however, the inventors seek to improve the
pull-out resistance of fibers from concrete while avoiding the kinds of
mechanical or physical fiber attributes that might otherwise impede the
ability of the fiber to be introduced into, and uniformly dispersed
within, the concrete mix. The present inventors believe that the clinker
intergrinding process of Vondran results in cement particles being ground
into, and embedded in, the fiber surface. Moreover, the deep-abrading
action of the cement clinker may be undesirable because the fibers will
tend to clump during humid conditions (e.g., storage, shipment) due to the
hydrating cement particles. Furthermore, fibers can not be interground
with clinker at high volumes using ball mill machinery in an
clinker-intergrinding process because the fibers would potentially clog
the classifier unit used in such mills for separating ground cement
particles from the grinding operation. The present inventors have also
discovered that fibers interground in ball mill operations using clinker
are severely abraded, and, in effect, are shredded to the point at which
their mechanical integrity, for purposes of reinforcing concrete, is
defeated. Such clinker-interground fibers, whether by abrasion and/or
impact of clinker material, lose mechanical resistance to pull-out from
concrete (i.e., fracture toughness) because the fiber bodies and ends are
shredded or devastated by the clinker/fiber intergrinding operation.
The terms "shredded" or "shredding" are used herein to refer to the
tearing-apart of the fiber body into smaller elongated pieces. The concept
of "shredding" as used herein is not equated herein with the concept of
"fibrillation". The concept of fibrillation may be seen to occur where a
multifilament fiber, comprised of two or more strands or fibrils are
adhered or bonded together, is separated into its component strands or
fibrils. On the other hand, "shredding" is defined for present purposes as
the act of breaking a fiber down (whether monofilament or multifilament)
into pieces smaller than the constituent strands or fibrils.
In view of the disadvantages of the prior art as discussed above, the
present inventors believe that a novel fiber for reinforcing matrix
materials, and in particular hydratable cementitious materials such as
concrete and shotcrete, are needed. Also needed are novel methods for
making such fibers and for modifying such matrix materials.
SUMMARY OF THE INVENTION
In contrast to the above-described prior art fibers and methods for
manufacturing reinforcing fibers, the present invention provides fibers
which are micro-mechanically-deformed such that the fibers are flattened
and have surface deformations for improved contact with the matrix
material. Fibers of the invention are mechanically-flattened to provide
macro-level deformations in terms of varying width and/or thickness
dimensions within fiber lengths, but are also "diastrophically" deformed
to provide micro-level deformations (e.g., microscopic material
displacements) on the fiber surface. This is achieved while avoiding the
obliterative clinker intergrinding process of the prior art.
The term "diastrophic," as used herein is defined in Webster's Third New
International Dictionary (Merriam-Webster Unabridged Dictionary,
Springfield, Mass.) as follows: an adjective "of, having reference to, or
caused by diastrophism." The term "diastrophism," in turn, is defined in
this Webster's dictionary as "the process of deformation that produces in
earth's crust its continents and ocean basins, plateaus and mountains,
folds of strata, and faults--."
The present application, therefore, borrows geological terminology in
describing "micro-diastrophic" synthetic fibers which have a microscopic
surface "diastrophism". After application of the flattening processes of
the invention, a number of physical deformations or material displacements
caused or induced in the fibers can be seen under the microscope to
resemble geological morphologies or phenomena. For example, the
microscopically viewed surfaces of the treated fibers have irregularly and
randomly elevated portions or ridges resembling islands, continents,
plateaus, and mountains; and there can also be detected equally random
folds of strata, faults (or fissures), and other physical displacements of
fiber material. These microscopic deformation irregularities appear
randomly on the surface of a given fiber, as well as from fiber to fiber.
Thus, the term "micro-diastrophic" is appropriate for describing the
microlevel deformations or physical displacements of exemplary fibers of
the present invention. The term "micro-diastrophism" also appears to
describe the three-dimensional morphological changes achieved by the novel
methods of the invention. These morphological changes may be achieved by
subjecting synthetic polymer material (preferably a polypropylene,
polyethylene, or mixture thereof) to a compressive force. An exemplary
compressive force may be achieved by using at least one roller, and
preferably opposed rollers to compress the fibers to induce irregular and
random microscopic surface deformations that are described herein as
diastrophic; this process is very different from superficially embossing
or crimping fibers. Alternatively, though less preferably, the effect may
be achieved by using a ball mill (without the use of cement clinker as
taught by Vondran et al). The stress forces on the fibers should be
sufficient to flatten the fibers in a manner to increase and vary (within
the length of the fiber) the fiber width dimension, thickness dimension,
or both; and to cause or induce micro-diastrophism in the fiber surface as
mentioned above. The micro-diastrophism in the fiber surface causes an
increase in the total fiber surface area that can be placed into contact
with the matrix material. The micro-diastrophic surface deformities should
be achieved without substantially shredding the elongated body or end
portions of the fibers (e.g., without cement particles being embedded in,
with attendant abrasion of, the fiber surface), although a small amount of
fibrillation or shredding at the extreme fiber ends may be tolerated
within the spirit of the present invention.
One advantage of the fibers of the invention is their ability to provide
strong bonds with the matrix material (e.g., concrete). This is believed
to arise from the fibers having a variable width and/or thickness
dimension(s), and enhanced bonding surface due to micro-diastrophism in
the fiber surface. These advantages are provided while avoiding a
substantial increase in fiber-to-fiber entanglement or clumping which
would otherwise be expected to arise during or after mixing into the
matrix material. Another advantage of the invention is that, in the
absence of using the prior art clinker-intergrinding method, the fibers
and methods of the present invention are substantially free of embedded
cement/clinker particles and the abrasive and obliterative shredding
caused by the prior art clinker-intergrinding operation.
Thus, the present invention provides high performance fibers and methods
for reinforcing matrix materials against cracks without entailing the
problems of prior art reinforcing fibers. Exemplary fibers of the
invention comprise a plurality of mechanically-flattened fibers having
generally elongate bodies, opposed body ends defining a fiber length, said
fiber bodies have varied width and/or thickness dimensions and having
micro-diastrophic surface deformities. Matrix materials and structures
comprising such fibers are also disclosed and claimed. An exemplary method
of the present invention for manufacturing fibers comprises providing a
plurality of synthetic polymer fibers, and mechanically flattening these
fibers to the extent that the fibers, after said mechanical flattening,
have a varied width and/or thickness dimension and micro-diastrophism.
Further advantages and features of the invention are further described in
detail hereinafter.
BRIEF DESCRIPTION OF EXEMPLARY DRAWINGS
An appreciation of the advantages and benefits of the invention may be more
readily apprehended by considering the following written description of
preferred embodiments in conjunction with the accompanying drawings,
wherein
FIG. 1 is a before-and-after diagram of a single polymer fiber untreated
(10) and an exemplary single polymer fiber treated by a preferred method
of the present invention (12);
FIG. 2 is a before-and-after diagram of a multipolymer blend fiber
untreated (20) and an exemplary multipolymer fiber treated by a preferred
method of the present invention (22);
FIG. 3 is micrograph of a side view of a single polymer fiber (untreated);
FIG. 4 is a micrograph of a side view of a multipolymer blend fiber surface
(untreated);
FIG. 5 is a micrograph at higher magnification of a multipolymer blend
fiber surface (untreated) of FIG. 4;
FIG. 6 is a micrograph of the surface of a single polymer fiber after
intergrinding with cement clinker in a ball mill (prior art method);
FIG. 7 is a micrograph of a shredded multipolymer blend fiber after
intergrinding with cement clinker in a ball mill (prior art method);
FIG. 8 is micrograph of a shredded multipolymer blend fiber surface
embedded with cement particles after intergrinding with clinker in a ball
mill (prior art method);
FIG. 9 is a micrograph of exemplary micro-diastrophic surface deformations
of a single polymer fiber treated by the method of the present invention;
FIG. 10 is a micrograph of exemplary micro-diastrophic surface deformations
of a multipolymer blend fiber treated by the method of the present
invention;
FIG. 11 is a micrograph of the edge view of an exemplary single polymer
fiber (shown adjacent to open cells of adhesive mounting substrate used
for handling fiber during viewing) treated by the method of the present
invention;
FIG. 12 is a micrograph of exemplary micro-diastrophic deformations on
surface of a multipolymer blend fiber treated by the method of the present
invention;
FIG. 13 is a micrograph of exemplary micro-diastrophic deformations on
surface of a multipolymer blend fiber treated by the method of the present
invention (tiny whitish specks are believed to be fiber polymer "dust");
and
FIG. 14 is a micrograph along an edge of an exemplary multipolymer blend
fiber treated by the method of the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The present inventors believe that the fibers of the present invention may
be used in a variety of compositions and materials and structures made
from these. The term "matrix materials" therefore is intended to include a
broad range of materials that can be reinforced by the fibers. These
include adhesives, asphalt, composite materials (e.g., resins), plastics,
elastomers such as rubber, etc. and structures made therefrom. Other
matrix materials include hydratable cementitious compositions such as
ready-mix concrete, precast concrete, masonry mortar and concrete,
shotcrete, bituminous concrete, gypsum-based compositions (such as
compositions for wallboard), gypsum- and/or Portland cement-based
fireproofing compositions (for boards and spray-application), and other
hydratable cementitious compositions, whether in dry or wet mix form.
A primary emphasis is placed upon the reinforcement of structural concrete
(e.g., shotcrete) however, since concrete (whether poured, cast, or
sprayed) is an extremely brittle material which presents challenges in
terms of providing reinforcing fibers which (1) can be successfully
introduced into and mixed in this matrix material and (2) can provide
crack-bridging bonding strength in the resultant concrete structure.
Prior to a detailed discussion of the various aforementioned drawings and
further exemplary embodiments of the invention, a brief discussion of
definitions will be helpful to facilitating a deeper understanding of
advantages and benefits of the invention. As the fibers of the invention
are envisioned for use in the paste portion of a cement or concrete (terms
which are sometimes used interchangeably herein), it is helpful to discuss
preliminarily the definitions of "cement" and "concrete."
The terms "paste," "mortar," and "concrete" are terms of art: pastes are
mixtures composed of a hydratable cementitious binder (usually, but not
exclusively, Portland cement, masonry cement, or mortar cement, and may
also include limestone, hydrated lime, fly ash, blast furnace slag,
pozzolans, and silica fume or other materials commonly included in such
cements) and water; mortars are pastes additionally including fine
aggregate (e.g., sand); and concretes are mortars additionally including
coarse aggregate (e.g., gravel, stones). "Cementitious" compositions of
the invention thus refer and include all of the foregoing. For example, a
cementitious composition may be formed by mixing required amounts of
certain materials, e.g., hydratable cementitious binder, water, and fine
and/or coarse aggregate, as may be desired, with fibers as described
herein.
The fibers of the present invention are preferably comprised of at least
one synthetic polymer (e.g., a polyolefin) and more preferably a
"multipolymer" blend which comprises two or more polymers (e.g.,
polypropylene and polyethylene; polypropylene and polystyrene). While
exemplary fibers of the invention may comprise a single polymer such as
polypropylene, the more preferred embodiments may comprise monofilaments
which have two or more polymers, such as polypropylene and polyethylene,
or other polymers having different moduli of elasticity. A suitable
multipolymer blend fiber is disclosed, for example, in World Patent Appln.
No. WO 99/46214 of J. F. Trottier et al., which is incorporated herein by
reference. Exemplary fiber material is also commercially available from
East Coast Rope Ltd., of Syndey, Nova Scotia, Canada, under the tradename
"POLYSTEEL". Fibers which can be used in concrete, for example, includes
any inorganic or organic polymer fiber which has the requisite alkaline
resistance, strength, and stability for use in reinforcing hydratable
cementitious structures. Synthetic polymer materials are preferred.
Exemplary fibers of the invention are synthetic materials such as
polyolefins, nylon, polyester, cellulose, rayons, acrylics, polyvinyl
alcohol, or mixture thereof. However, polyolefins such as polypropylene
and polyethylene are preferred. Polyolefins may be used in monofilament,
multifilament, collated fibrillated, ribbon form, or have shapes or
various sizes, dimensions, and arrays. Fibers may be coated, using the
materials taught in U.S. Pat. No. 5,399,195 of Hansen (known wetting
agents) or in U.S. Pat. No. 5,753,368 of Berke et al. (concrete bonding
strength enhancement coatings). It is suspected by the present inventors
that the use of different polymer molecular weights (e.g., a broad range)
may be advantageous in helping to obtain varied width and/or thickness
dimensions and a highly irregular surface morphology.
Preferred fibers are provided in "monofilament" form. The term
"monofilament" refers to the shape of the treated fiber which is provided
(literally) as "one filament" (ie. a unified filament). The term
"monofilament" as used herein does not preclude the possibility that the
singular filament may, when subjected to agitating forces within a
concrete mix (e.g., one having fine and/or coarse aggregates), break down
further into smaller filaments or strands when subjected to the agitation,
for example, in a concrete mix due to the comminuting action of aggregates
(e.g., sand, stones, or gravel). The term "monofilament" is used in
contradistinction from the term "multifilament" which refers to a bunch of
fibers that are intertwined together or otherwise bundled together such
that they have a plurality of separate strands. (To large extent, a fiber
can be defined as either monofilament or multifilament depending upon
whether one is able to visually discern the separate fibrils at a certain
point in time). In any event, the fibers and methods of the present
invention are contemplated to include, and to be applicable to, both
monofilament and multifilament fibers. The methods of the present
invention are also believed to be suitable for use with fiber precursors
(e.g., fibrillatable sheets), fibrillated fibers, and fibers assembled
into units such as intertwined fiber bundles, rope, or braided cords which
can be subjected to mechanical flattening and micro-surface deformations.
A preferred embodiment of the invention pertains to "multipolymer" fibers.
It is believed by the present inventors that such fibers (having two or
more different polymers, such as a mixture of polypropylene and
polyethylene or a mixture of polypropylene and polystyrene, for example)
provide better pull-out resistance from hydratable cementitious matrix
materials (e.g., ready mix concrete). It is surmised that the different
moduli of the polymers increases the chance of obtaining the variable
width or thickness dimensions and surface deformations desired. Also, the
use of multipolymer fibers better demonstrate the superiority of the
methods of the present invention when compared to the prior art
clinker-intergrinding process (taught by Vondran), because the destruction
and shredding of multipolymer fibers under the prior art Vondran method is
highly discernible both to the naked eye and under microscopic
magnification.
Generally, the fibers of the invention may be cut into desired lengths
before or after mechanical flattening. Fibers for reinforcing matrix
materials preferably (after cutting) have average lengths of about 5-75
mm; average widths of 0.5-8.0 mm.; and average thicknesses of 0.005-3.0
mm. It is possible to exceed these preferred limits without straying from
the spirit of the present invention. The length, width, and thickness
dimensions may depend on the nature of the fiber material and use
contemplated (e.g., polyolefin, carbon, polyamide, etc.) and the matrix
material contemplated for reinforcement (e.g., concrete, asphalt, plastic,
glass, composite material, rubber, latex, adhesive, etc.). The unique and
novel morphologies of the fibers of the present invention are intended to
be used over a range of fiber and matrix materials, although the greatest
challenge and the predominant purpose of the present invention is to
provide fibers having at least one synthetic polymer, and preferably at
least two ("multipolymer") polymers blended together, for reinforcing
hydratable cementitious matrix materials such as concrete.
Exemplary fibers of the present invention may be made by subjecting a
plurality of fibers, or one or more fiber precursors (e.g., a polymer
sheet cut or scored to provide "fibrillated" fibers, a bundle of
monofilaments, continuous monofilament(s) or multifilament strands that
is/are subsequently cut to the desired length, etc.) to deform the width
and/or thickness dimensions, preferably to provide a macro-level keying
effect through width and/or thickness dimensions that vary along the fiber
length by at least 5%, more preferably by at least 10%.
FIG. 1 is an illustration of an untreated polypropylene fiber 10 when
viewed under microscope. The untreated fiber 10 has an essentially uniform
width dimension (w) along its entire length. When a plurality of such
fibers 10 is introduced randomly between opposed rollers and flattened a
few times by reintroducing the fibers randomly between the rollers, the
fibers become substantially flattened 12, particularly at the opposed ends
14, where the end width (w') can be seen to be substantially greater than
some of the narrow body width sections (e.g., w"). Moreover, while the
untreated fiber 10 will be seen under microscope to be generally
translucent, the variably flattened fiber 12 will be seen to be less
translucent due to internal and superficial stresses (generally indicated
by the lines drawn as at 16) which can be more readily appreciated when
viewed at higher magnification.
FIG. 2 is an illustration of an untreated multipolymer fiber 20 comprising,
for example, a blend of polypropylene and polyethylene. After mechanical
flattening, the flattened fiber 22 demonstrated a width increase at the
fibers ends 23 and less translucence which indicated internal and
superficial stresses (26).
FIG. 3 is a micrograph taken at 33.times. magnification of an untreated
single polymer (polypropylene) fiber. The uniformity of width dimensions
can easily be viewed.
FIG. 4. is a micrograph taken at 45.times. magnification of an untreated
multipolymer blend (polypropylene/polyethylene) fiber. This also
demonstrates a fairly uniform width dimension. At this magnification,
slight striations in the surface can be detected, and these features are
believed to be due to the effect of the extrusion die used to form the
fiber. FIG. 5 is a micrograph taken at higher magnification (4500.times.).
The striations can now be seen a small but relatively uniformly shaped
grooves between relatively smooth polyblend (polypropylene/polyethylene)
fiber. This also demonstrates a fairly uniform width dimension. At this
magnification, slight striations in the surface can be detected, and these
features are believed to be due to the effect of the extrusion die used to
form the fiber. FIG. 5 is a micrograph taken at higher magnification
(4500.times.). The striations can now be seen as small but relatively
uniformly shaped grooves between relatively smooth polymer surfaces of the
fiber. A large groove or channel is seen running diagonally upwards from
left comer to right comer of the micrograph, and this is believed to be
due to polymer separation in the multipolymer blend.
FIG. 6 is a micrograph taken at 50.times. magnification of a polypropylene
fiber subjected to intergrinding with cement clinker in a small
laboratory-scale steel ball mill. This is the effect of the prior art
Vondran process. The surface is embedded with cement particles (large
whitish areas.) The width dimensions are not substantially varied by the
ball mill clinker intergrinding. In any event, the present inventors
attempted to simulate the ball mill process without the use of a ball mill
as actually used in grinding cement clinker, because they do not believe
that any fibers would actually be left if an actual ball mill for clinker
intergrinding (i.e. actual cement manufacture) were used as taught by
Vondran.
FIG. 7 is a micrograph at 50.times. enlargement of a multipolymer fiber
(polypropylene/polyethylene) that was subjected to the prior art Vondran
clinker intergrinding process in a ball mill. The fiber was shredded and
abraded by the action of the clinker material during intergrinding. (The
edge of a piece of tape can be seen in the micrograph; this was used to
handle the fiber during viewing). The integrity of this fiber is
obliterated and rendered essentially useless for purposes of reinforcing
cementitious materials. This shredded fiber would likely cause
fiber-to-fiber entanglement and mixing difficulties.
FIG. 8 is a micrograph at 900.times. magnification of a multipolymer fiber
subjected to clinker-intergrinding. The embedded cement clinker particles
can now be more readily seen embedded into the fiber surface. The nature
and severity of the shredding can be more readily appreciated, because
extremely tiny microfilaments (many less than 5 um) can be seen to have
separated completely from adjoining fiber material, and this is believe to
be an impediment to the task of reinforcing concrete.
FIG. 9 is a micrograph at 900.times. magnification of the surface of a
single polymer (e.g., polypropylene) fiber flattened in accordance with
the methods of the present invention. A plurality of fibers were flattened
a number of times by random introduction through opposed rollers. The
fibers were compressed such that they had variable width and/or thickness
dimension(s) (as will be shown later), but most significantly the fiber
surfaces had micro-diastrophic features. Readily seen are elevated or
raised portions, ridges, mountain-like "terrain," as well as depressions,
folded strata (there is a round-shaped folding seen near the upper left
corner of the micrograph), as well as irregular and random fissures or
breaks in the material. This microscopic diastrophism can be seen as an
increased surface area. Such micro-diastrophic change in the fibers cannot
be achieved merely by placing fibers between embossed rollers to cut or
roughen the surface, but can only be achieved by exerting sufficient great
pressures on the fibers to achieve irregular and random displacement or
dislodgment of masses of the fiber polymer material.
It is with reference to micrographs such as provided in FIG. 9 that one can
sense the metaphoric or poetic appropriateness of the definition of
"diastrophism" as provided in Webster's Third New International
Dictionary: "the process of deformation that produces in earth's crust its
continents and ocean basins, plateaus and mountains, folds of strata, and
faults--." For example, the reference to "ocean basins" seems especially
appropriate for the fiber surface morphology shown in FIG. 9, because the
elevations and depressions of physical fiber material as shown are
fluid-like in the manner of an ocean floor, or they otherwise suggest or
resemble glacial erosions or shifting.
FIG. 10 is a micrograph at 900.times. magnification of a multipolymer
(polypropylene/polyethylene) blend fiber that was treated in accordance
with the flattening process of the invention. The micro-diastrophism seen
is also random, showing elevated peaks and depressions of fiber material.
Irregular elevated ridges can be seen to span over depressions and/or
fissures of discontinuous micro-fractures in the polymeric material. The
polymer material can be said to be "smeared" and physically displaced by
the flattening process of the invention in an irregular, non uniform
manner.
FIG. 11 is a micrograph taken at 40.times. magnification of an edge view of
a single polymer (polypropylene) fiber (shown adjacent to open cells of
adhesive used for handling the fiber) that was flattened in accordance
with the method of the present invention. The thickness dimension can
easily be seen to vary along the fiber length, and the micro-diastrophic
surface deformations along the edge are suggested by light reflecting off
the surface edge.
FIG. 12 is a micrograph across the width of a multipolymer blend
(polypropylene/polyethylene) fiber treated by the method of the present
invention. The width varied from 1.57 to 1.73 mm at one point, while the
micro-diastrophic deformations of the surface could also be appreciated.
FIG. 13 is a micrograph at 2,500.times..times. magnification of a
multipolymer blend fiber (polypropylene/polyethylene) treated by the
flattening process of the present invention. The whitish specks (about 5
um or less) are bits of polymer from the fiber which are not believed to
defeat the ability of the fiber to bond with matrix materials such as
concrete, asphalt, or other materials. The micro-diastrophism can be seen
to include discontinuous stress-fractures between and among areas of
continuities (plateaus or ridges) of varying elevations which are shown
with different shading in the micrograph of FIG. 13.
FIG. 14 is a micrograph at 190.times. magnification of an edge of a
multipolymer blend fiber flattened by the process of the present
invention. The thickness of the fiber varied at points, from 173 um, to
161 um at another point, and to 152 um at yet another point. (A tape
substrate is depicted at the left of the picture; this was used for
handling the fiber). Towards the right of the micrograph, there are
elevated portions of the fiber surface that are visibly evident in the
distance. The surprising micro-diastrophism induced in the fiber surface
(or face on the edge-to-edge side) can be especially appreciated by the
micrograph of FIG. 14. Particularly remarkable is that the flattening
stress force, which is applied against the fiber, induces both a
noncontinuous micro-fracture (i.e., a fissure of finite length) as well as
elevated ridges in the displaced polymeric fiber material.
Exemplary methods of the invention provide fibers having varying widths
and/or thickness dimensions and micro-diastrophism in the fiber surface. A
preferred method comprises exerting a compressive force on fibers,
preferably by using the compressive action of at least one roller, and
more preferably by cooperative action of opposing rollers, to compress
fiber material to the point at which the fiber materials is physically
displaced first on a macro-level (affecting the general shape or profile
of the fiber as evident to the unaided human eye) and, second, on a
micro-level whereby the microscopic fiber surface morphology is altered to
include irregular and random elevated portions and "fissures" (or
discontinuous stress-fractures) in the polymer material.
Preferably, at least one roller or series of rollers is/are rotated upon a
stationary surface or conveying surface upon which the fiber material or
fiber precursor is situated. The fiber material may be supplied in the
form of continuous fibers, which may be cut after flattening, or pre-cut
fiber lengths; or they may be supplied in the form of fibrillatable or
scored sheets or braided or interwoven sheets, ropes, cords, etc. Thus, an
exemplary method comprises introducing a plurality of cut fibers (e.g.,
average length of 5-75 mm) randomly between opposed rollers, such that
fibers can be pressed against each other as they pass between opposed
rollers. More preferably, the fibers are subjected to such flattening at
least two or more times between the same rollers or other rollers. For
example, fibers may be subjected to a series of opposed rollers, each
roller having increasing textured surfaces for achieving microscopically
sized displacement of polymer material (micro-diastrophism) on the fiber
surface.
Rollers are preferably steel. As polymer synthetic fibers are generally
provided having equivalent diameters (or thicknesses) of average 0.5-1.0
mm, the steel rollers may be set apart at a distance somewhat less than
this (say about 0.01-0.3 mm), depending upon the nature of the fiber
material, ambient temperature, and other processing conditions. An
exemplary method of the invention, therefore, comprises feeding a
plurality of fibers or fiber precursors, either in an uncut or cut state
(e.g., average 5-75 mm), between the opposed steel rollers to provide
macro-level deformation as well as micro-diastrophic deformation on the
fiber surfaces.
In preferred processes, the varied widths and/or thicknesses of the fibers
can be achieved by varying the distance between opposed rollers (or
between roller and other contact surface between which fibers are passed);
by using textured rollers whereby the texture is operative to provide a
varied compressive force sufficient to achieve random physical deformation
in the fiber shape; and/or by subjecting two or more overlapping fibers
randomly between opposed rollers. The present inventors also believe that
macro-level and micro-level deformations may be obtained in the fibers by
hitting the fibers randomly, or conveying fibers in a random fashion,
under hammers or other objects capable of compressing certain portions of
the individual fibers with sufficient stress forces.
The inventors have also discovered other surprising ways of achieving the
desired deformation morphology and micro-stress-fracturing in the fibers
using rollers. One way is to alter the surface of at least one roller,
such as by roughening the surface by using it to crush brittle materials,
such as stone, gravel, clinker, and the like; and then subsequently
introducing fibers between rotating rollers wherein at least one, and
preferably two or more, of the rollers have the roughened surface. Such
surface-roughened or "textured" roller surfaces should preferably have a
random structure or pattern, although it is possible to have the rollers
textured with a irregular or non-uniform patterns (e.g., dimples,
protrusions, grid patterns, line patterns, raised portions, indentations,
grooves, or a combination thereof) against which or between which (as in
opposed rollers) the fibers may be (preferably randomly) compressed,
deformed and/or fractured.
In still further exemplary processes of the invention, the fibers may be
introduced to the deforming action of rollers more than once, or,
alternatively, may be subjected to a succession of rollers (preferably
with each set of rollers inducing a greater degree of deformity and/or
micro-fracturing compression force).
Another process of the invention comprises conveying a continuous strand or
strands of fibers between compressive force micro-diastrophic-inducing
means, such as rollers or hammers, whereby the fibers are flattened along
the length of the fiber, and then cutting the fiber strand or strands such
that individual fibers are produced having varied widths and/or
thicknesses along the individual fiber length. Less preferably, the
flattening of the fibers can be accomplished by using steel balls in a
rotating mill or container without clinker or cement particles being
interground, and thus without subsequently having embedded cement
particles on the fiber surfaces; this is less preferable, as the ability
to obtain variable width and/or thickness dimensions in the individual
fibers is much more difficult to control.
The present invention also includes matrix materials, such as asphalt or
cementitious compositions, incorporating the exemplary fibers described
herein, such as concrete compositions comprising a binder, a fine
aggregate and/or coarse aggregate (and fibers). Accordingly, exemplary
compositions include the fibers of the invention in a matrix material such
as concrete, ready-mix concrete, masonry concrete, shotcrete, bituminous
concrete, and structures made from these compositions, including
foundations, walls, retaining wall segments, pipes, slabs, decks, surface
coatings, and other building and civil engineering structures. Asphalt
compositions containing fibers of the invention, as well as structures
made from such compositions, such as roads, surfaces, decks, walks, patch
materials, and the like, are also within the present invention. The
compositions may be supplied in either wet or dry form. These would also
include dry and wet compositions comprising shotcrete or other
spray-applicable materials, such as gypsum and/or Portland cement-based
fireproofing, and their coatings and coated structures.
The invention also pertains to packaged fibers wherein a plurality of the
exemplary fibers described herein are packaged in average fiber lengths of
5-75 mm within a container, such as a bag, peripheral bundle wrapping,
capsule, box, carton, adhesive, wetting agent, bonding agent, or other
packaging means that is operative to hold the fibers together, whereby
their total outer surface area is diminished to facilitate introduction of
the fibers into the cement or concrete mix, and whereby their uniform
dispersion within the matrix material is facilitated. When introduced into
the matrix material (and subjected to agitation, water, heat, or other
initiating condition therein), the packaging material can be made to
dissolve, abrade, rupture, or otherwise disrupt, thereby releasing the
fibers into the mix and allowing them to present a larger total surface
area to become mechanically engaged with the matrix material.
In the concrete arts, a package suitable for accomplishing this is
available from Grace Construction Products, Cambridge, Mass., under the
registered tradename CONCRETE-READY BAG.RTM.. This packaging comprises a
non-water-soluble paper. Other packaging, which may be water-soluble, such
as polyvinyl alcohol, may also be employed for purposes of the present
invention.
Fibers may also be bundled by using an abradable or dissolvable perimeter
wrap as taught in U.S. Pat. Nos. 5,807,458 and 5,897,928 both owned by 3M
of Minnesota. Alternatively, fibers may be releasably adhered together
using a water-soluble adhesive or wax or other releasable inter-fiber
bonding agent, such that the individual fibers may become separated and
dispersed uniformly during agitation of the cement mix.
It is preferable to subject the fibers, whether in cut or uncut state, or
fiber precursors (e.g., fibrillatable or scored sheets) to compressive
stress forces in a dry state (although known wetting agents or
surface-active agents can be used to decrease static charge) and
preferably at or below ambient (room) temperature before the fibers are
coated or packaged. Treatment of the fibers using the techniques of the
present invention is best accomplished when the fiber material is near,
at, or below room temperature to induce micro-diastrophism in the fiber
material, (observable under microscope -e.g., at 5.times.-4000.times. or
more magnification). In other words, at the risk of belaboring the point,
if the fiber material is subjected to compressive stress when the fibers
are warm (e.g., after extrusion), then the fiber material can be
resiliently compressible rather than brittle and may not be caused to
deform by operation of the rollers or other flattening means. Rather,
after extrusion, the fibers should be allowed to cool (or otherwise should
be chilled) before being subjected to compressive stresses sufficient to
induce macro-level width or thickness variability as well as
micro-diastrophism in the fiber surface structure.
In one exemplary method of the invention, fiber material is continuously
fed (in continuous strands, although cut strands can be used) between
steel rollers, whole surface is textured by prior crushing of stones and
gravel, to cause flattening and varying of the width and/or thickness
dimensions and further to cause the fibers have micro-diastrophism in
their surfaces. The fibers may optionally be coated (such as with a
conventional wetting agent, anti-static coating material, bonding agent or
other coatings as may described above), before or after flattening; then
they can optionally be bundled together such as by a peripheral wrap
and/or interfiber bonding materials, and then optionally cut (if needed)
into shorter average fiber lengths (with the average fiber length, for use
with cementitious materials, preferably in the average range of 5-75 mm).
An exemplary method of the invention for making the aforementioned fibers
comprises subjecting a plurality of synthetic polymer fibers to flattening
forces so as to create varying width and/or thickness dimensions and to
diastrophically deform the fiber surface, without substantially embedding
concrete particles into such surfaces and without substantially shredding
the opposing ends and elongate bodies of the fibers.
An exemplary method of the invention for modifying a matrix material, such
as a cementitious composition, comprises introducing into the matrix
material the above-described exemplary fibers of the invention. The fibers
are preferably contained within a packaging means operative to minimize
initial total surface area of the fibers and also operative, upon
agitation of the material mix, to dissolve or abrade or disrupt the
packaging and release the fibers into the matrix material mix.
Thus, an exemplary method for reinforcing hydratable cementitious materials
comprises: adding to a cement, mortar, cement mix, or concrete mix (dry or
wet), in an amount of 0.05-15% weight based on percentage volume (of total
dry solids) the above-described exemplary fibers of the invention. The
composition is then mixed to obtain a concrete, mortar, or paste mix in
which the individual fibers are released from the packaging and
homogeneously distributed within the mix. The mix is then cast into a
configuration or structure. More preferably, the addition amount of fibers
is 0.1-5 vol. %, and more preferably 0.5-2 vol. %, based on concrete. The
term "configuration" means and refers to a foundation, a rectangular
shaped slab, a wall, a block, a segment of a retaining wall, a pipe, or
portion of a civil engineering structure, bridge deck, tunnel, or the
like.
A preferred embodiment of the present invention comprises a plurality of
fibers having the exemplary macro-level and micro-level deformations
described above, which fibers are bundled (either physically or by wetting
agents) and/or packages (such as in a disruptable or dissolvable
container) to minimize initial total surface area of the fibers (to
facilitate introduction into and dispersal of the fibers within the matrix
material). Upon agitation of the material mix or by operation of the water
in the mix, bundling and packaging becomes either abraded or dissolved or
otherwise disrupted, thereby releasing fibers into the mix and allowing
the micro-diastrophically deformed fiber surface area to contact the
matrix material (e.g., concrete, shotcrete mix, gypsum wallboard material,
sprayable fireproofing, etc.).
For application into a concrete matrix material, as one example, the
plurality of fibers may be separately bundled and/or packaged together
within bags or containers, such as Grace Concrete Ready-Bag.RTM. packaging
as previously described.
EXAMPLE 1
Comparative Physical Data
The present inventors do not believe that polymer fibers subjected to the
Vondran method, employing clinker in an actual industry cement
manufacturing ball mill, would have any residual integrity, but would be
obliterated after intergrinding. Thus, they attempted to reproduce in
their laboratory an intergrinding process that would leave a fiber with
some semblance of its form, for comparative purposes. The ball used had a
one cubic foot capacity and was loaded with about 22700 grams weight of
steel balls having diameters between 12 and 17 mm on average and about
2400 grams total weight of cement clinker having diameters between 0.01
and 0.1 mm. About 100 grams of fibers was loaded into the mill, which was
then operated at 45 revolutions per minute for a period of 30 minutes.
Polypropylene fibers available from 3M and multipolymer (e.g.,
polypropylene/polyethylene) blend fibers available from Grace Construction
Products were used. Such multipolymer fibers are generally commercially
available. The micrographs of these fibers (untreated) were provided in
FIGS. 3 and 4, respectively.
If the ball mill operation is run for a period of time that is less than
what is required for grinding clinker into cement, the results may be
typified by FIG. 4a, which shows the ends of the interground fiber
substantially shredded apart. The inventors even attempted to repeat the
ball mill intergrinding operation using cement particles alone without
clinker, but the fibers were also severely damaged and contained embedded
cement particles. Micrographs of fibers, when treated by the cement
clinker intergrinding ball mill method, were provided in FIGS. 6 and 8
(single polymer) and FIG. 7 (multipolymer).
As seen in the micrographs of FIGS. 7 and 8, when fibers were interground
with clinker in a ball mill, the fiber surfaces are abraded and embedded
with cement clinker. As shown in FIG. 8, in particular, the fiber is
shredded to the point at which the fiber integrity is essentially
destroyed.
EXAMPLE 2
Micrographs of fibers treated by exemplary flattening methods of the
present invention are provided in FIGS. 9-14. The surfaces contain
micro-diastrophic material displacements and contain no embedded clinker
and have no substantial shredding (e.g., complete separation of fibrils or
strands that destroys the physical integrity of the fiber). The fibers
were treated by introducing a plurality of fibers randomly, often
overlapping one another, between opposed steel cylinders which were spaced
apart a distance that was less than the fiber thickness, such that
physical flattening occurred in the general shape of the fiber and
micro-diastrophism occurred on the surface of the fibers. It is believed
that the distance between opposed rollers was about 10%-50% the average
diameter dimension of the fibers. The macro-level and micro-level
deformations perceived were especially pronounced when a multipolymer
blend fiber (Grace Structural Fiber) was subjected to the method of the
present invention, and passed between the rollers at least two or three
times.
It is surmised by the inventors that the various surface portions of fibers
treated by the flattening method of the present invention will demonstrate
fractal geometry in the sense that the irregular and random
micro-level-deformities (micro-diastrophism) will appear at increasingly
higher magnifications of the surface.
The present invention is not to be limited by the foregoing examples which
are provided for illustrative purposes only.
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